In addition to the excellent posts made in the other thread, here's an essay I wrote previously on the subject.
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Biogeography Establishes Evolution Beyond a Reasonable Doubt
One of the most impressive lines of data unambiguously supporting common descent comes from the field of biogeography. Simply put, biogeography is the study of the geographic distribution of species and ecologies (
short primer).
If the common descent of life is correct, there will be not only anatomical, fossil, molecular, embryonic, etc. continuity between different species, but
geographic continuity as well. This science generally takes two forms when applied to evolutionary biology.
1. Species are Geographically Distributed by Proximity to Common Ancestors
TalkOrigins
notes that "A reasonable nonevolutionary prediction is that species should occur wherever their habitat is. However, macroevolution predicts just the opposite--there should be many locations where a given species would thrive yet is not found there, due to geographical barriers..."
In other words, if common descent was true, species distribution
should follow the specific and highly unlikely nested hierarchy of common descent we observe in taxonomy, the fossil record and other lines of evidence,
not functional redundancy, aesthetics, ideal environment,
or other design-oriented patterns.
For those who might not understand this, evolution predicts we will find species
distributed by geographic dispersion from ancestral forms, not by ability to live in environment or other criteria an intelligent designer would likely use. Their modern distribution will logically be a result of their common origin.
For example, two species of near-identical monkey will be found in close geographic proximity to each other,
even if they're ideally suited for environments across the ocean as well. Deserts will have unique groups of plants that nevertheless appear more similar
to each other than
plants in distant deserts with the same exact environment.
Islands will contain a large number of endemic wildlife that, while potentially possessing unique adaptations,
will be most closely related to life on the nearest mainland than the flora and fauna of
distant islands with virtually identical environments.
"... American, Saharan and Australian deserts
have very similar habitats, and
plants from one grow well in the other. However,
indigenous Cacti only inhabit the Americas, while
Saharan and Australian vegetation is very distantly related (mostly Euphorbiaceae)."
This is a startling, unintuitive and
amazingly successful prediction.
"The Galapagos Islands west of South America and the Cape Verde Islands off west Africa have similar tropical environments. But, their native plants and animals are not closely related; instead, they closely resemble the flora and fauna of their respective nearby large land masses."
The best correlation between accepted phylogeny and biogeography is inevitably drawn from species
that have the most trouble dispersing. Animals that can fly long distances are perhaps the hardest to track using biogeography, as they can spread like wildfire from one area to another and leave a confused pattern behind. Certain flowering plants and lumbering, non-marine animals
are ideal, however.
As a variation of this, we can also predict where species should
not be found. For example, limited knowledge of the geographic distribution of the elephant, coupled with the fact that it's a large, heavy animal that can't cross large bodies of water, predicts they will
never be found on Pacific islands, even though the environment is ideal for them. Similarly, remote islands will have a distinct lack of amphibians, which can't easily travel there.
This is exactly what we observe. Islands that are very distant from a mainland demonstrate complex, interrelated ecosystems which are nevertheless composed of species that can travel long distances and/or traverse the water. This indicates their ecology, which can be considerably different than the mainland, was constrained in its evolution by having access only to easily dispersing species.
This is extremely unlikely to come true if common descent is false and those species were specially created, because the pattern it requires is very specific. Out of the quadrillions of possible geographic distributions possible, only a select few will be compatible with evolution.
As TO notes,
"Closely related species could be distributed evenly worldwide, according to whichever habitat best suits them. If this were the general biogeographical pattern, it would be a strong blow to macroevolution..."
The single best example of evolutionary biogeography goes, hands-down, to Australian marsupials. Together they comprise a diverse and incredible range of animals from kangaroos to "mice" to "wolves", but--and this is amazing--they're
much closer related to each other other than their near identical-looking counterparts in placental mammals!
Extinct Tasmanian Wolf, mounted in a museum 
North American Wolf
At a glance, these are nearly indistinguishable. Going by a design explanation, one could infer this extinct creature should be genetically and anatomically most similar to the more familiar type of wolf.
It's also suitable for the same environment--that of the roaming hunter. Either the wolf or the Tasmanian Wolf could replace each other and remain a viable species in their newfound environments.
Let's see another marsupial vs. placental grouping.
Australian Flying Phalanger, a.k.a. Sugar Glider
Vs.
North American Flying Squirrel
Again, pretty much the same animal in two different versions. You would expect them to be similar in a design explanation, since they're obviously created to do the same thing.
But wouldn't it come as a surprise to learn that the Tasmanian Wolf and Sugar Glider, which occur on the same continent but otherwise occupy niches as different as one could find between any two species,
share more in common than the two wolves... (?!)
Wesley Edwards expands on this.
"In the table below, keep in mind that all of the animals in the Marsupial column are more closely related to each other than they are to their counterparts in the other column. This is an extremely telling observation; it really should make you say, 'Wow!'
Consider that the Tiger cat is more closely related to the marsupial mouse than it is to the Bob Cat, which looks superficially almost the same. The same can be said about the Tasmanian Wolf, which looks almost identical to a "regular" wolf, but is also in fact a closer relative to the Marsupial mouse, who for all the world looks like a 'regular' mouse. Placental ========== Marsupial Code:
Wolf Tasmanian Wolf
Flying Squirrel Flying Phalanger
Mouse Marsupial Mouse
Mole Marsupial Mole
Anteater Numbat
Bob Cat Tasmanian Tiger Cat
Lemur Spotted Cuscus
Startling. Totally inconsistent with intelligent planning and common sense, yet actually
predicted by unintelligent jury-rigging of an ancestral, geographically isolated marsupial into these widely varying (and unfilled) niches by the forces of evolution.
2. Paleontological Correlation Between Biogeography and Independent Phylogenies
If the above mentioned facts alone aren't enough to establish common descent as a fact with evidence rivaling that of a round earth, we also have
independent corroboration from the fossil record.
We know for, example, that the earliest marsupial fossils we find are from the Late Cretaceous, and they apparently originate in North America. Plate Tectonics, an independent science,
tells us that Australia was connected via Antarctica to North America back then.
What is the logical deduction that follows if common descent is true? Well, it's very simple--the earliest proto-marsupials
must have travelled to their current habitat via Antarctica. Thus, we should expect to find fossils of primitive, extinct marsupials
in Antarctica, where they travelled on their way to a new continent, despite the fact that
very few creatures in general live there now.
"Interestingly, we have found marsupial fossils on both South America and on Antarctica. This is an astounding macroevolutionary confirmation, given that no marsupials live on Antarctica now..." -
TalkOrigins
Similarly, Darwin himself used insights in biogeography to
predict ancient fossil hominids in Africa.
"The special case of biogeography pertinent to human evolution, of course, is that in 1871 Darwin used the work of Huxley and others which showed that humans most resemble chimpanzees and gorillas who live only in Africa to predict where we would most likely find fossils of our own earliest ancestors - Africa.
That Darwin was correct is borne out... as, indeed, all of the earliest-known hominids are from Africa and nowhere else. But the fact that Darwin could use evidence from biogeography to predict what the pattern should look like in a completely separate body of evidence - the fossil record - is a wonderful example of how concordance among separate lines of evidence is both a testable prediction of a scientific theory and further support for a theory - in this case, evolution - when the prediction is borne out."
Besides the validity of common descent, there is basically
no obvious reason why early hominid fossils should be unique to the exact area predicted by it.
The Global Flood Falsified?
It stands without mention, of course, that biogeography also falsifies the creationists' global flood. As described in Genesis, it would catastrophically destroy terrestrial biogeography, and the subsequent recovery would rearrange it
so that our reconstructions would point to the Middle East as the origination point of all extant species.
Instead, we observe temporal continuity between complex, interdependent ecosystems going back since long before humankind was around.
It strains credibility to the breaking point to suggest that all marsupials (which includes agile and slothful creatures alike!) would simultaneously run off as a whole to Australia after disembArking (pardon the pun),
but no other mammals would follow them. That cacti would fly off to the New World instead of colonizing Middle Eastern deserts, while other plants and creatures ran off to South America but not Africa and Europe.
And that, once they got there, they established the same, complex, interdependent ecosystems found in their respective geographic location's pre-flood fossil record; and they even managed to leave behind extremely unlikely, (presumably) fake evidence for evolution, too!
Summary - Organisms in the earth's biosphere are geographically distributed by relatedness, not ability to survive in the environment, functional redundancy or other in-advance design-oriented goals--exactly as evolution would predict.
- Analysis of modern distributions of various species allows us to predict, with startling accuracy, where fossils of their common ancestors will found. This is a startling confirmation of the explanatory and predictive power of evolution.
- The temporal and geographic continuity biogeography indicates, as well as the fact it irreconcilably contradicts a recent origin of all extant organisms from the Middle East, is quite fatal to the global flood hypothesis.
Without common descent, these patterns in the geological distribution of organisms (by evolutionary relationships), which correlate extremely well with independent lines of evidence like fossils, genetic sequence analysis and comparative anatomy, are wholly baffling. With it, they're natural, expected and predicted in a most elegant, parsimonious manner.
Linear Mode
